How do you know if a water pump is bad i have an 02 subaru outback changed thermostat radiator cap and flushed the cooling system however the temp climbs on hills and when car is under a load then tem?

Usually the water pump failure is by leaking. Although it is possible that a failure of the impeller is causing your problem, my experience is that it is more likely a partially clogged radiator. Try opening the Windows, turn the heater all the way to hot, fan on high, when the engine is overheating. If the temperature comes back down, the radiator is probably the culprit. Had a similar problem with my 2000 Forester after a failed head gasket had leaked oil into my cooling system. That gunk just doesn't flush out. --Ken